In the practice of English language teaching, great importance is attached to writing ability of second language learners. There are many difficulties existing in second language writing, and a variety of writing appr...
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In the practice of English language teaching, great importance is attached to writing ability of second language learners. There are many difficulties existing in second language writing, and a variety of writing approaches aim to help students solve these problems. The process approach has now attracted most attention.
The present research tries to find out the role of pre-writing activities, which is advocated by the process approach. It has been found out that these activities mainly help students develop meaning in their writing although different students reacted in a different way. And they also help students begin their writing more easily.
Another finding is the role of the teacher. They are expected to: 1) regard students as writers; 2) guide through pre-writing stage; 3) integrate receptive skills and productive skills. This research suggests the need for writing instruction by which students can experience writing as a creative process for exploring and communicating meaning.
Growth cones are highly motile structures at the end of neuronal processes, capable of receiving multiple types of guidance cues and transducing them into directed axonal growth. Thus, to guide the axon toward the app...
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This paper describes the generation of gradients having complex shapes in solution using microfluidic networks. Flowing multiple streams of fluid each carrying different concentrations of substances laminarly and side...
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This paper describes the generation of gradients having complex shapes in solution using microfluidic networks. Flowing multiple streams of fluid each carrying different concentrations of substances laminarly and side-by-side generated step concentration gradients perpendicular to the direction of the now. Appropriately designed networks of microchannels for controlled diffusive during of substances generated a range of shapes for the gradients, including linear, parabolic, rind periodic. The lateral dimensions of the gradients ranged from 900 to 2200 mum. This paper also demonstrates the generation of overlapping gradients composed of different species. Since solutions in the microfluidic network exist as steady states and are continuously renewed, the gradients established in the capillaries are spatially and temporally constant and can be maintained easily for periods of hours. Using laminar now to generate gradients should be useful in both biological and nonbiological research.
A method of locating crop rows in image sequences is described. Unlike several previously reported algorithms, the method does not rely upon the segmentation of plant material from the background on the basis of absol...
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A method of locating crop rows in image sequences is described. Unlike several previously reported algorithms, the method does not rely upon the segmentation of plant material from the background on the basis of absolute brightness or colour. Rather, the periodic amplitude variation due to parallel crop rows is exploited. Given the geometry of the camera arrangement and the crop row spacing, a filter is derived which allows the crop rows to be extracted whilst attenuating the effects of partial shadowing and spurious features such as weeds. The position and orientation of the rows are tracked using an extended Kalman filter. The method has been used to guide a mechanical hoe in winter wheat with an RMS positional error of 15.6 mm at a speed of 1.6 ms-(1), despite the presence of complex shadows cast by the tractor in the imaged area. (C) 2000 Elsevier Science Ltd. All rights reserved.
Proteoglycans influence aging and plasticity in the nervous system. Particularly prominent are the chondroitin sulfate proteoglycans (CSPGs), which are generally inhibitory to neurite outgrowth. During development, CS...
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Proteoglycans influence aging and plasticity in the nervous system. Particularly prominent are the chondroitin sulfate proteoglycans (CSPGs), which are generally inhibitory to neurite outgrowth. During development, CSPGs facilitate normal guidance, but following nervous system injury and in diseases of aging (e.g., Alzheimer's disease), they block successful regeneration, and are associated with axon devoid regions and degenerating nerve cells. Whereas previous studies used non-nervous system sources of CSPGs, this study analyzed the morphology and behavior of sensory (dorsal root ganglia) neurons, and a human nerve cell model (SH-SY5Y neuroblastoma cells) as they contacted nervous system-derived CSPGs, using a variety of microscopy techniques. The results of these qualitative analyses show that growth cones of both nerve cell types contact CSPGs via actin-based filopodia, sample the CSPGs repeatedly without collapse, and alter their trajectory to avoid nervous system-derived CSPGs. Turning and branching are correlated with increased filopodial sampling, and are common to both neurons and Schwann cells. We show that CSPG expression by rat CNS astrocytes in culture is correlated with sensory neuron avoidance. Further, we show for the first time the ultrastructure of sensory growth cones at a CSPG-laminin border and reveal details of growth cone and neurite organization at this choice point. This type of detailed analysis of the response of growth cones to nervous system-derived CSPGs may lead to an understanding of CSPG function following injury and in diseases of aging, where CSPGs are likely to contribute to aberrant neurite outgrowth, failed or reduced synaptic connectivity, and/or ineffective plasticity. Microsc. Res. Tech. 54:273-286, 2001. (C) 2001 Wiley-Liss, Inc.
In order to suppress residual vibrations, a general method is presented for preconditioning any guidance function prior to its application to a dynamic system, by convolving it with a sequence of impulses. The approac...
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In order to suppress residual vibrations, a general method is presented for preconditioning any guidance function prior to its application to a dynamic system, by convolving it with a sequence of impulses. The approach includes first the development of the necessary design specifications for the impulse sequence, so that the robustness properties cover the widest possible variation of the system natural frequencies. Three solution methods are proposed then, with special emphasis in the achievement of the minimum possible duration time of the impulse sequence. Numerical experiments verify the effectiveness of the robustness, not only with respect to variations of the natural frequency, but also with respect to variations of a range of other linear and non-linear variables.
The paper presents the relations that form the basis for the calculus models needed to study rolling guided missiles. The equations of the general motion are written within the Resal trihedral in a way that allows, af...
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The paper presents the relations that form the basis for the calculus models needed to study rolling guided missiles. The equations of the general motion are written within the Resal trihedral in a way that allows, after linearization, one to draw up a structural scheme of the controlled object, a scheme that will be used in the guided missile system analysis. Opposite to the flying machines with stabilized roll where the analysis is done after decoupling the channels, for the missile with rotation, the analysis of the scheme is done simultaneously on both channels, as terms used are complex terms. Furthermore, there will be presented some characteristics of this type of missile by analyzing a model close to the one of an antichariot missile with gasodynamic control.
The development of systematic methods for materials and process selection is a relatively new field. The variety of materials and processes available to the engineer, as well as the complexity of the set of requiremen...
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The development of systematic methods for materials and process selection is a relatively new field. The variety of materials and processes available to the engineer, as well as the complexity of the set of requirements encountered in industrial situations, are the driving forces behind the development of software aiming at the guidance of the designer. Born as pedagogical tools, such software, tailored for a given class of materials or of applications, has now in certain cases reached a degree of specialization that is mature and applicable to the industrial design process.
The theory in this paper is motivated by the problem of aircraft guidance in automatic flight control, in which plant models are nonlinear. This leads us to consider the stable inversion problem, which in turn can be ...
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The theory in this paper is motivated by the problem of aircraft guidance in automatic flight control, in which plant models are nonlinear. This leads us to consider the stable inversion problem, which in turn can be cast as the problem of finding a bounded solution of a time-varying nonlinear system subject to a bounded input. Under the appropriate assumptions there is a unique bounded (for all time) continuous solution to this time-varying nonlinear system in response to the bounded (for all time) input. We show that there is a (local) stable manifold containing-all bounded continuous solutions for non-negative time, and that all such solutions converge to the aforementioned unique solution as time: goes to infinity. Likewise there is a (local) unstable manifold containing all bounded solutions for non-positive time and these converge to the unique solution as time goes to minus infinity. In fact, the unique solution (cross the time axis) is the intersection of the stable and unstable manifolds. (C) 1999 John Wiley & Sons, Ltd.
To assess the value of accurate preoperative CT-guided needle localization of occult breast lesions, we reviewed a total of 39 needle-directed biopsies of breast tumors in 24 women. The average age was 52.9 years (ran...
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To assess the value of accurate preoperative CT-guided needle localization of occult breast lesions, we reviewed a total of 39 needle-directed biopsies of breast tumors in 24 women. The average age was 52.9 years (range 31-67). All lesions were nonpalpable and mammographically, as well as sonographically occult. They were solely seen on MR-images. After demonstrating the suspicious region on CT scans, a hookwire was inserted. The correct position was confirmed by a control scan. The subsequent histo pathological examination showed that 28 of the lesions (71.8%) were benign, among them mastopathy, fibrosis, fibroadenoma, papilloma, intramammary lymph node, liponecrosis and epitheliosis. Eleven lesions (28%) were malignant and showed either lobular, ductal or tubular cancer. Our results endorse that CT guided needle localization is a helpful method that allows a precise surgical excision of the suspect area with the removal of a minimal amount of breast tissue, (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.
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